198 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



induce no changes, the changes noted being due merely to the operation on the 

 animal. But these protein substances continue to exert their effects after they 

 have been subjected to treatments which deprive homoiogenous differentials of 

 their characteristic influence. (3) Likewise, protein substances, such as those 

 present in blood serum of strange species, exert a homoiogenous effect; (4) 

 on the other hand, blood plasma of a different species exhibits the effects of 

 true heterogenous differentials, probably because of the presence of fibrinogen. 

 (5) Lastly, there are strange substances of a non-protein nature; these are de- 

 void of any specific action and behave like autogenous substances. But again, 

 in contrast to autogenous substances, non-protein substances are non-specific. 



It might be of interest also to compare the local reaction elicited by ordinary 

 foreign bodies with that induced by substances carrying autogenous, homoiog- 

 enous or heterogenous organismal differentials. The material which possesses 

 individuality or species differentials, after introduction into the subcutaneous 

 tissue, exerts a combination of two effects: (1) non-specific foreign body 

 effects and (2) specific effects elicited by the individuality and species differ- 

 entials 



It will therefore be necessary to analyze the differences between the reac- 

 tions against a foreign body and the more specific reactions against living tis- 

 sue. The reactions of the host cells against the foreign body do not show those 

 fine gradations which are elicited by the individuality and species differentials. 

 Variations observed in the reactions against foreign bodies depend largely 

 upon mechanical factors which distinguish different kinds of material, but 

 there are also some slight differences in the mode of reaction shown by differ- 

 ent host species. Common to all these foreign body reactions is the prominent 

 part played by the connective tissue cells of the host; they move towards the 

 strange material and attempt to invade and to make it into a part of the host 

 by transforming it into fibrous tissue. They first surround the periphery and 

 then turning at a right angle invade it, branching off in tree-like fashion ; they 

 act as though they were stimulated and activated by the foreign material. In 

 contrast to the farther distant connective tissue, which tends to assume a 

 resting condition, forming collagen fibers, the connective tissue directly ad- 

 joining the foreign body remains cellular. However, the soil into which these 

 host cells have penetrated is injurious to them and after a certain time they 

 are apt to perish ; their fibroplasm and nuclei become admixed to the foreign 

 material, such as 1% agar, and thus a new substratum consisting of a com- 

 bination of disintegrating cellular material and the fibroplasm-agar-mixture is 

 produced; into this other host cells penetrate and ultimately accomplish its 

 organization. In the peripherpy of the foreign body and also in its fissures 

 there may also collect giant cells of various sizes, and mononuclear cells, the 

 nature of which is uncertain, but which may perhaps represent either modified 

 connective tissue cells or monocytes. It seems that giant cells with their ac- 

 cumulation of nuclei and their increase in cytoplasm form especially in 

 those places in which there is an obstacle to the progress of the host cells, as 

 in furrows in the foreign body. All those cells, the giant cells as well as the 

 mononuclear cells, or cells transitional between these two, possessing two 



